Field of the Invention
The present invention relates to image erasing methods, image erasing apparatuses, and conveyor line systems using the image erasing apparatuses.
Description of the Related Art
Recently, an image processing apparatus using a thermoreversible recording medium has been incorporated into and utilized in a conveyor line system which needs to manage a conveying container (e.g., returnable container employed in a physical distribution system). The thermoreversible recording medium is attached on the conveying container as a label and is rewritable with laser beams emitted from the image processing apparatus in a non-contact manner. This eliminates a need for attaching and peeling off a label, which makes it possible to efficiently operate the conveyor line system.
The thermoreversible recording medium contains, for example, a leuco dye and a reversible color developer. When the thermoreversible recording medium is heated to equal to or higher than a coloring temperature range in which the leuco dye and the reversible color developer melt and then rapidly cooled, the thermoreversible recording medium turns into a colored state (visible state). Meanwhile, when the thermoreversible recording medium is heated to a decoloring temperature range, which is lower than the coloring temperature range, held for a predetermined period of time, and then cooled, the thermoreversible recording medium turns into a decolored state (invisible state). However, even though the thermoreversible recording medium is heated to equal to or higher than the coloring temperature range in order to develop a color, if thermoreversible recording medium is then slowly cooled, the thermoreversible recording medium turns into the decolored state.
The thermoreversible recording medium having such property as described above is problematic in that, under a high temperature environment, the thermoreversible recording medium is decreased in coloring density since the thermoreversible recording medium which has been heated is difficult to be rapidly cooled. On the other hand, under a low temperature environment, there also is a problem that the thermoreversible recording medium is decreased in the coloring density since the thermoreversible recording medium is difficult to be held within the decoloring temperature range after the thermoreversible recording medium is heated.
In order to solve the above problems, there has been proposed a method for controlling laser beam power depending on a surface temperature of the thermoreversible recording medium (see, Japanese Unexamined Patent Application Publication No. 2008-194905).